I'm playing through fallout 4 on survival, and just got access to combat shotguns; they do more damage than the double-barreled shotgun, but they lack the sawn-off upgrade to increase critical damage. My Gun Nut perk is currently capped at 2 for several levels, so I only have access to the Calibrated receiver, not the Calibrated Powerful Receiver.
I use the shotgun to critically hit powerful enemies who get close. Will I deal more critical damage with the combat shotgun, sacrificing the critical bonus for more base damage?
I read in another thread that Calibrated Receivers double critical damage, but I don't know if the Sawed-off mod is a further doubling, or works differently.
Best Answer
I can't find a definitive reference showing that the sawed-off barrel doubles critical damage, but that's what the receivers with that description do, so for the rest of this post we're operating under the assumption that it does so.
In that case, all you need to do is compare the base damage of the two guns, once you have the mods attached. The sawed-off will do four times its listed base damage (assuming you have no other modifiers, such as the better criticals perk), whereas the combat shotgun will do only double the base damage.
Therefore, the combat shotgun will do less critical damage, unless its listed base damage is at least twice as much as the sawed-off.
Looking at the stats on Nukapedia, it looks like the sawed-off with a calibrated powerful receiver would do 79 base (plus various modifiers your character has that would also apply to the combat shotgun). It looks like the combat shotgun with calibrated reciever would do 50.
So, if you're just using the shotgun for an occasional critical, stick with the sawed-off.
Lucky Effect
That being said, I think you have other options.
Any gun with the Lucky legendary modifier, such as the easily obtainable Righteous Authority, also doubles critical damage. Put a calibrated receiver on it, and it's doing 4x critical damage, just like your sawed-off shotgun.
Lucky also increases the rate at which criticals are generated, and essentially every gun has a bigger clip than the sawed-off. This means you can use this as your main rifle, and also as your critical trump card. It's also more friendly to your carrying capacity.
I highly recommend you at least try this out, as an alternative to the shotgun. Unless of course you've found a Lucky Double-Barrel Shotgun. That would be pretty lucky.
Notes on Attachments
I no longer waste perks on crafting perks like Gun Nut. You can easily find attachments on found guns or in stores, and remove them and put them on your gun. It's not uncommon to find attachments better than you'd be able to craft anyway.
Instead, invest those perks in combat, so that your gun works even better, with the same attachments as if you'd spent the perks on crafting.